Art of making hydraulic cements, &amp;c.



.- UNITED str-Atr s PATENT OFFICE.

WILLIAM H. HARDI G, or PHILADELPHIA, PENNSYLVANIA.

ART .OF MAKING HYDRAULIC oEMEN'rs, ac.

l Specification of Letters Patent. Application filed April 30, 1903. Serial No. 430,162.

Patented Dec. 29, 1908.

To all whom it may concern:

Be it known that I, WILLIAM H. HAR- DING, a citizen of theUnited States, anda:

resident of Philadel hia, in the county of Philadelphia and S tate of Pennsylvania, have invented certain new and useful Improvements in the Art of Makin Hydraulic ements, &c., of which the following. is a specification.

My present inventionrelates more spe" cifically to the production of Portland cement, though certain of its features and advantages may be utilized in connection -With other processes involving the decomposition of minerals and the fritting or clinkering of the nonvolatile products of such decomposition.

The production of Portland cement necessarily Involves the fritting or clinkering of an alkaline base, such as lime (CaO) with an .acid of the class typified by silica (SiO and alumina (A1 0 Usually, the lime, silica, and alumina are all. present in certain proportions, and the limits of variation in the percentage 'of each are now well recognlze in the art. As the constituent materlals are not found in nature in a free state, they are commonly prepared for the clinkering process by the burning of raw materials containing compounds thereof in suitable proportions and free from too great admixture of objectionable materials or elements which might interfere with the process or deteriorate the quality of the cement product. If the natural materials available do not contain the constituents inproper proportion, a suitably proportionedmixture may be prepared either by using different materials, each containing one or more desired constituents, or by combining a material containing,too great a proportion of one constituent with another material conthe total unavoidable waste.

rial, containing agreater lime content thanis necessary for Portland cement is used in connection with so-called cement rock, clay, or other material containing an excess of silica,-the proportions being such that the mixture when calcined and fritted or clink-,

ered, will consist of a compound containing tri-calcium silicate and alum nate. According to the universal practice, these raw materials are finely ground and intimately mixed, either wet or dry, prior to heating them to drive ofi' the carbon dioxid' and -Water from the lime, silica, and alumina. The double process, first of decarbonizing the calcium carbonate and dehydrating the silica and alumina, and, second, frittlng or clinkering the resulting lime,- silica, and 1 alumina so that they may unite in the proper relation to form what is commonly su posed" to be a solid solution of calcium si 5 lcat'es, aluminates, etc., is now-and alwa s has beenperformed by a single heat, bot when the urning is done in an u right kiln and when it is done in a rotary ki 11. It has long'been recognized that the upright kiln is not well adapted for clinkering and that the rotary Z kiln is uneconomical, and it was proposed to completely dry and calcine thematerial in an upright kiln and then clinker it in a rotary kiln; but rior to my invention this method has been ound to be practically impossible, I

and no one has ever succeeded in applying it commercially. Moreover, the proposition has been declared unsound, because the rotary kiln requires such reat heat at the lower end for clinkering t at any amountwhich can,be absorbed in calcining further up the kiln' is insignificant as com ared'with he result has been that the single burning operation 'with continuous calcining and clinkering in a rotary kiln has gradually-become. recognized and generally accepted as the standard modern method of making Portland cement, so that now practically all of the Portland cement made in this country is produced by this method, and the use of the upright'kiln for Rosendale cement has been due mainly to the demand fora cheaper, 'lower grade cement and to the" prexistence of the upright kiln plants and the expense involved in-sub stituting rotary kilns.

My resent lnvention consists of'amethod where y the raw material instead of being calcined and clinkered at one heat, resub- .je"cted to v two distinct burning operatlons m Portland cement clinker.

clinker fu the kiln.

such manner and, under such conditions as have proved highly practical and economical, as well as productive of a good" quality of 'Heretofore, it has been supposed that the method of burning cement 1n a rotary kiln would be improved if the decarbonization of all of the materials'were made perfect before any of it is exposed to-a clinkering temperature, but according to my experience with my process in which this is an easily obtainable condition, it is desirable that there be some uncalcined material, even though it be an extremely small percentage which remains to be decomposed 1n the rotary kiln, preferably so as toabsorb heat at or near the region where the intensity of-the;applied heat begins to approach a temperature sufficient to y calcined material, to the end that the material shall not be too fully clink ered at a point too far up the kiln, as' this would result in subjecting the clinker to clinkering temperature for too long a time. In fact, the chnkeringoperation in the continuous feed rotary kiln is most easily accomphshed where the decarbonizing or calclmng reactlon is prolonged so that it will be taking place to some extent at least at or near the time and place where the clinkering process commences, so that the two processes succeed each other or even overlap or intermingle in the sense that certain particles may be undergoing decarbonization at points not too remote from other particles which are sintering or fritting to form the clinker. One reason'for this may be that the clinkering operation, wherein the alkaline lime at high temperature unites with the acid silica and alumina, is, theoretically at least, an exothermic or heat evolving o eration and, in any event, is one which oesnot involve appreciable absorption. of heat, whereas the operation of driving off the carbon dioxid from the calcium carbonate, though occur- I1I 1g&t a lower temperature, is an endothermic reaction which does involve great absorption of heat. It seems probable that a certaln amount of the heat absorbing o eration of driving off carbon dioxid is bene cial,

insomuch as its refrigerating efiect must tend to temper the heat evolving operation of cllnkerlng, and if this had no other effect, it would tend to localize the clinkering zone nearer the discharge end of the kiln, and thus to shorten the time between beginning of chnkering and discharge of the material from This may be of considerable importance, insomuch as clinkering is a critical operation so far as concerns time and temperature. When performed in a rotary kiln, it requiresthat the material be raised to a temperature commonly supposed to be be- I tween 2500 and 3000 degrees Fahrenheit, in

order that the union of the materials may be sufliciently, complete and yet the temperaquires.

dioxid (CO evolved in the clinkering kiln,

and the initialpercentage is preferably such that under the s ecial conditions of use, the last remnant of t e CO is driven olf and the heat absorbing reaction terminated at the proper time to give the best results. vantage of my method is that the initial percentage of uncalcined material necessary for this urpose in any given kiln, may be accurate y predetermined. For any given percentage, the distribution or region of activity of its heat absorbing reaction may be further controlled by adjusting the heaviness of the feed and the rate of its travel therethrough. In general, it may be said that in all cases the clinkering by my method will be more rapid than by the old method with the uncalcined rock.

In the preferred practice of my method wherein I use previously calcined material containing only the required percentage of uncalcined rock, the work which the heat must do is similar in kind, though less in amount than the work which is performed in the last 20 or 30 feet of a rotary kiln operating by the old process on uncalcined material, so that for the practice of my method, the length of the kiln need be only that necessary to do the required amount of chemical work, plus the length necessary for heating up the materials to. the calcining temperature. Hence, an old fashioned short kllll is amply adequate for my purposes, though a kiln to 100 feet or more in length may be employed and is even desirable in case the material employed for my purposes contains an' exceptionally large percentage of unburned or partially burned material.

Another feature of my invention consists in regulatingthe supply of the material to the upper end of the kiln and the rate of feed therethrough, so that the feed shall be, heavy; that is to say, so that the amount of material lying on the upturning side of the kiln shall be equal to or greater than the amount of such material commonly found in the ordinary rotary kiln process, where uncalcined rock is used.

Another feature of my invention consists in burning the coal at the ordinary rate employed for raw uncalcined rock, or even at a considerably higher rate, and then utilizing the resulting heat by increasing the heaviness of the feed and the rate of travel of the material to a point where the increased amount of material operated upon, compensates for the decreased work which a given volume re- In this Way the full jet will supply no more heat than is necessary for the amount of material operated upon. This requires that the rate of travel of the material down Anad.

and separate clinkering by another burning was first proposed, thejets used in the rotary kilns were either atomized oil jets or producer gas jets. The latter. has always proved'difficult of use for clinkering operations, because of the low heat intensity of the flame. On the-other hand, the, oil jets as used inlrotary kilns have always. been proportioned and designedto produce a very ine tense heat which would necessarily overburn the clinker unless restrained insoiine way, as

by a dominant heat absorbin reaction continuing far down the kiln.-

previously uncalcined-,'.raw materials, which could be .ma'nipulated so -,aso distribute the heat absorbing de'carbonjization.

of the lime, to any extent.

Oneof the meritorious features of myin vention consists in the discovery that one of the varieties of fuel and. one of the forms of j et-burner now in common use is suitable for f the practical performance of the'clinkering part of my process. The fuel which I use is very finely pulverized'and carefully dried gas coal carrying approximately 30% .to 38% volatile matter. This fuel is usedin connection with a low pressurediffuse burner of the McAuley type, supplied with air by. a rotary fan. I prefer this to the high velocity et of the Hurry and Seamans type,which is supplied from an air compressor, because with the low pressure type the flame is more localed-a't the lower end of"the*kiln. Moreover, the fuel itself has a comparatively narrow range of temperature, which extends entirely hrough the range of temperature necessary for clinkering, and yet does not extend far above that range. Thus it is easier to limit and temper the clinkering of my precalcined material to prevent serious overburning. It will be noted that the Specific fuel and burner used and the method of its use contribute to localize the region of clinkering temperature close to the lower end of the kiln, thus operating in a manner tending to produce a general effect contributory to the above described effect of the carbon dioxid in the material in the upper portion of the kiln.

It will be een that the percentage of 00,,

believe that" this is' one of the reasonswhy no one hasever succeeded in using this .lintensely hot flame for clinkering, except-in 'connection overbu'rning of' the clinker as would make my process impractical. Hence, the degree and extent to which the one expedient must be utilized will depend upon the extent and effectiveness with which the others are utilized, and considerable variation and substituticn of one for the other to produce the same result will be possible and desirable under varying circumstances and conditions.

It will be obvious that the resent full disclosure of the various ossih e subsidiary or contributingfactors wi 1 enable those skilled in the art to successfully utilize one or more of these factors to the exclusion of the others. In attempting any such variations, considerable caution should be exercised, particularly in the matter of attem ting to completely calcine the material be ore subjecting it to the final heat in the rotary kiln, because the absence of carbonic acid as in the material wonderfully facilitates t 1e operation in a the rotary kiln, and at the same time the heat insuring the presence of some uncalcined rock or'some other adequatelheat absorbing ,work in the rotary kiln, the clinker may be overburned. In fact, the great facility with which com letely decarbonized material becomes over urned in the rotary kiln, is one of the causes which has heretofore made the double burning operation practically impossible' of successful performance, and it is with a view to controlling and tempering or localizing the clinkering, instead of with a view to facilitating it, that I have devised my 1 present process wherein I make adequate use of some and preferably of all of the herein dc scribed tempering factors.

I will now describe an illustrative applicament rock in lumps of the size commonly supplied from the quarry, may be charged together into an upright kiln of the Rosenda e type, preferably in such proportionate quantities as are indicated by analysis as necessary to furnish the ercentages of lime, silica, alumina, etc., desired in Portland cement 'clinker to be roduced therefrom. The rock is charged in ayers of 7 to 8 inches thick, a thin layer of coal being distributed tion of my processes practiced with certain specific raw materials: Lime rock and ceover the top of each layer of rock in quanti ties hardly sufficient to cover the same. The kiln is referably of the continuous type, thelayers ein added at the top and the burned -materia removed at the ottom at suitable intervals. spect to the amount of coal used and the The' practice. with retime of burning and the draft employed are material for the practice of my method of clinkering in the rotary kiln. The limits are so wide that in certain cases the burning may be in accordance with the very best practice in the burning of Rosendale cement, thou h for m purposes I find it is chea er to use aout haf or two-thirds as much uel in the upright kiln as is used for Rosendale cement, or else to draw the kiln about twice as fast, since I find that the rockcan be about two-thirds to three-quarters burned with an expenditure ofabout half of the amount of fuel required for complete burning, and such burning is sufficient for my purposes. As alternative to the above, the cement rock ma be burned alone in a Rosendale kiln, while the lime rock is burned in a separate kiln, which may be of the ordinary type employed for burning lime. In either case the product-of the upright kilns isin condition to be ground with very small ex ense for power and the grinding may be as e as desired. The finely ground and thoroughly mixed material containing the proper portions of lime,.silica, and alumina, and the desired percentage ofunburned, calcium carbonate 1s fed into an'o'rdinary 60foot rotary cement kiln about seven feet invdiameter,

having preferably a very small incline or pitch, say to. i mch to the foot, and rotatmg at arelatively high speed of one revolution in 30 to 45 seconds. The feedin of the material at the u per end. is preferab y such as to :maintain a heav layer of material on the upturning side 0 the kiln. The pur- .pose of this is to. expose only a small proportion of the material at a time, the mam body of the material being shielded b the'outermost layers.- The purpose of t e rapid rotation is. to rapidly. shift the material so that each portion will receive a brief exposure to the heat on the surface and will then be tumbled over and covered u ,the net result being :a rapid succession of rief exposures. As the material travels down the kiln, it is heated up to the calcining teinperature-and.

the cont1nued, thorough agitation results in completion of the calcining operation and the ultimate clinkeri-ng after. the manner hereinabove described. The' low pressure burner the diffuse flame is preferably projectedinto impingement with the material on the upturm'ng side of the kiln.

- In order that the fuel economies and other advantages made possible by. my method,

maybe more fully understood, I will set forth the following-specific details as to one,

unburned stone and heating an than usual.

articular. case of practice of the process. v

ime rock and cement rock in proportion to yield a Portland cement with rather less than the usual percentage of lime, were charged into a Rosendale kiln in lumps as received from the quarry. The lime stone was a proximately pure calcium-carbonate. T e amount ofcoal used was equal to about 32 pounds per barrel 'of the roduct. After urning in the usual way, tie product was found to average about 55 to lime and about 10% of the stone was uncalcined. This product was ground to a fine mesh and thoroughly mixed, was then clinkered in an ordinary rotary kiln 60 feet in length. A low pressure powdered fuel burner was emloyed, such as was commonly used on that lriln for raw,. unburned material. When used in the ordinary way on unburned material, the output of this kilncommonly averaged about 170 barrels per day, with a fuel consumption of 110 pounds of coal per barrel. When used to clinker the above described 'product of the Rosendale kiln, the burner was operated'so as to burn a somewhat greater amount of coal per hour and the amount of material fed into the kiln at the u per, end. was such that the output of clinker was ap roximately. 525 barrels for my material cinkered. by my rocess, as

against. 170 barrels for the raw roc clinkered by the old process.

The coal required in the rotary kiln for calcining the 10 war cent. of

olinkering all, of it, Was found to be 46 pounds per, barrel. The kiln was rotated at slightly greater speed than usual, and the heaviness of the feed on the upturning side was greater The fuel consumption and ex ense by my method com ares with the ol method as follows: In t e rotary kiln I burned some- What more coal, but I got more than three times the output, andthe actual consumption of 46 pounds per barrel by my method as against the 110 pounds per barrel by the old method, leaves me a margin of about 64 pounds of coal to cover the fuelex ense for preliminary burning in the upright iln. As a matter of fact the upright kiln consumed onlyabout half of this margin, that 15, 32

pounds, and, moreover, this 32 pounds was cheaper coal, costing only half as much per ton as the gas coal.

From the above it will be seen that by my process, I used 42% of 110 pounds in the rotary kiln and 29% of 110 ounds in the upright kiln, so that my total uel consum tion was 71 per cent. of 110 pounds. As t e 29 per cent. used in the upright kiln was obtainable at half the price of the gas coal used in the rotary kiln, the actual cost of the total coal burned by my process was 56% per cent. of the cost by the old process.

The fine grinding of the hard rock required by the 'old rocess was, of course, fanmore ex ensive t anthegrinding of my partially ca cined material.

The Portland cement clinker thus pro- .duced Was of good quality and assayed ap-- proximately s ica alumina and iron oxid 10%, lime 59%, magnesia 34 .The above details relate to a particular twenty-four hour run of the rotary kiln by my rocess, and the rotary kiln used was not uilt specially for the urpose. It will be understood, therefore, t at the above is not an ideal case. I

It be observed that by "roperly pro-' portioning the length of the iln and the eaviness-and rate of the feed to the amount of fuel burned, the work to be done upon the materialby' the heat may always be made to bear such relation to the time of exposure and to the distribution and iintensity of the heat that the material will not reach thev clinkering temperature until it has approached within a predetermined desired distance from the discharge outlet of the kiln, and thus the time of exposure to the clinkering temperature and the duration" and mtenslty of the clinkering reaction, may be accuratel predetermined so as tosecurethe best resu ts. I v

As I have above indicated, the work to be done includes the heating up of the material followed by the heat absorbing operation of driving ofi the Water and any remaining carbon dioxid from such portion of the rock as has not been previously calcined. Though the calcinationmvolves great heat absorption and is one of the most eflective and easily applied expedients for tempering the process and preventing premature clinker ing, it is not essential inall cases and it will be evident from the spirit of my prior disclosure, that if the feed is made sufliciently heavy and the agitation sufiiciently rapid,

.. and if these are properly 'pro ortioned to the rate of feed, the length oft e kiln, and the intensityof the flame, so that all of the heat which can be transmitted to the material while traveling the required distance down the kiln, will be only sufiicient to do the work of heating up the material to the .chnkerlng tem erature by the time it arrives within-a suitab e distance from the discharge end or outletin.such case, the duration of [by the heat consists main of the preliminary wor the rotaryjkiln consisting in thedec'omposition the clinkering reaction may be redetermined and controlled even thou h t e work done Iy in-raisingtemperature of the materials without doing chemical work.

' One of the advantai s in making a part of calcium carbonate is that 'the"reactions within the kiln at the lower end and the various attendant visible phenomena are I 'more nearly analogousto those to which the done "by the heat inordinary cement burner has become. accustomed .in his prior experiences with rotary kilns, and hence he can'more easily learn to gage the situation and to conditions in the practice of my new process. Another great advantageis that the driving oiI of the lastremnants' of the CO from the calcium carbonate. requires a disproportion ate amount of fuel when accom lished-in the upright kiln, whereas the con itions in the of the heat, the presence of the uncalcined constituent or its equivalent is especially desirable. In any case other kinds of preliminary work requiring the absorption of heat may be used in combination with or as a substitute for the calcining reaction. Among the other kinds of work suitable for this pur osemay be mentioned the. evaporation 0 free water introduced or remaining in the mixture, or preferably the dissociation of combined water of crystallization from silica, alumina, iron oxid, or clay, in which they may be contained; or the distilling-off of potash, soda, or sulfur compounds. These latter reactions are especially eiiective in preventing overburning, insomuch as most of them occur at or near the clinkering point and involve chemical absorption of relatively large amounts of heat per unit weight. Hence, though the quantities may be very small, the tempering effect may be ver noticeable. 1

Where t e material is prepared from practically ure lime mixed with clay, the work done by the heat the rotary kiln,

aside of the heating up of the materials, may consist largely of driving off of Water of or stallization. J I

'W ere the chemical work done in the rotary kiln is largely that of calciningof a-remnant of calcium carbonate, this remnant'may consist of a constituent either of the cement rock or of the lime rock. Wherethe two are burned together in one kiln, as in one properlyvarythe instance above mentioned, thesaid-remnant of calcium carbonate is likely. to be contributed by the lime rock which is usually more "refractory than .the cement; rock. Where the lime rock and cement rockare calcined in separate kilns, it maybe desir- .able to completely calcine the lime rock and to get the desired percentage of calcium carbonate by under-burning the-cement rock.

In certain cases the lime rock and "the cement rock or,other raw materials may be I pose ofmore easily defining the nature of the completely calcined and dehydrated in the upright kiln, and then ground and mixed in proper proportions required for the Portland cement clinker. This -material, re uiring' practically no chemical work to be per ormed in the rotary kiln, may then be modified or, as it were, loaded by the addition of a certain amount of qreviously prepared mixture of raw materia calculated to furnish the required amount of calcining or other heat absorbing re-action inthe rotary kiln. This furnishes a convenient method of standardizing the operations of the plant, since a standard raw mixture may be pre ared which when addedwto the completely ca cined -mixture, will always give a standard, definite mixture to be acted u on by the heat in the rotary klln. While this method of preparing the material is convenient and certain, it

- necessarily involves the expense of complete may be varied so as tocompensate for a con calcination of the major portion of the material in the upright kiln. Hence, I prefer in actual 1practice to underburn as uniformly as possib e in the upright kiln, so as toget an approximately uniform product, and then to correct unavoidable variations by adding a variable amount of raw mixture.

In cases where it is found desirable to standardize the amount of heat absorbing work to be done in the rotary kiln, the raw mixture may be proportioned so as to contain the precise proportion of lime, silica, and alumina content required for the Portland cement, so that variable amounts of such raw mixture may be added without varying. the composition of the resulting clinker.

It will be undertsood that-Where standardization of the unburned content of the mixture is not attempted or is imperfect, the rate and heaviness of feed and the adjustment of flame and the amount of coal burned,

siderable range of variation in the mixture.

Certain features of the clinkering process as herein described and as set forth in certain of the claims depend mainly on the composition of the cement forming material, and so far as concerns such claims it is relatively unimportant what kind of kiln 01 other apparatus is used for artially or wholly calcining the calcium car onate content or for parv tially or wholly dehydrating the hydrated content of the material to be clinkered.

Moreover, so far as concerns the broader'subject matter, all the stepsof my process are independent of the specific form of the aparatus in which the operation is performed;

ence, except as therein otherwise definitely specified, the claims for the process are not limited tot'he specific'apparatus described in the specification. In certain of the claims wherein there is moreor less definite specification of apparatus, it will be understood that the apparatus is referred to for the purmaterial to bring it to the clinkering temper- 'ature.

In these cases the language is such as might be taken to imply that those factors which are predetermined or adjusted are the only variable factors and that the factors with respect to which they are adjusted are fixed. 'lhis classification of the factors is convenient and'natural insomuch as it assumes a properly proportioned plant already installed and ready for operation. Nevertheless, where it is desired that the practice of the process include the construction of a new plant or the alteration of an existing plant, the factors of pitch, diameter, and length of the kiln and the distribution and intensity of the heat within the kiln are equally convenient and desirable factors for variation or adjustment with reference to the others. The work which must be done on the material to bring it to the clinkering temperature is, of course, in all cases capable of variation by variation in the character of the constitutents of the material. Hence, it will be understood that where certain of these factors are specified in the claims as variable oradjustable with respect to certain other factors, such claims are to be considered as covering a process wherein any one or all of said factors are varied, adjusted, or predetermined for the described purposes, with reference to any one or all of the other factors. I

Lime rock and cement rock may be classed together for; some purposes and separately for other purposes. In nature they are frequently found in adjacent strata of the same formation, and in certain cases they may more or less overlap and merge into each other, (so that for resent purposes the distinction between t e classes may be considered as being largely functional with res ect to the specific operation of making Port and cement. Ihey both contain calcium carbonate and do not contain other materials in such amount and quantity as would have an objectionable effect on the composition ,of the Portland cement clinker to be made therefrom. The lime rock may be substantially pure calcium carbonate, or it may include rock having a smaller percentage of lime, provided the amount be in excess of the proportions suitable for the manufacture of cement, or it may include similar rock containing lime, silica, alumina, etc. but having the ercentage of lime too smallfor the desire quality of cement.

I claim the method which consists in charging fragmental lime rock and cement rock into an upright kiln, with a layer of coal for each layer of rock, the amount of the coal and the rate of combustion thereof being proportioned to the rock so as to effect the calcination of about two-thirds to nine-tenths thereof, grinding and thoroughly mixin the products of said 0 eration, and then 0 inkering it in a rotary ki 11.

2. In the art of making Portland cement, the method which consists in charging fragmental lime rock and cement rock, into an upright'kiln of the Rosendale type, with a layer" of coal for each layer of rock, the amount of the coal and the rate of combustion thereof being proportioned to the rock so as to effect calcination of about two-thirds to nine-tenths thereof; grinding and thoroughly mixing the burned material and preparing therefrom a mixture containing lime, silica, and alumina in proportions suitable for cement burning; feeding said material into a rotary kiln; generating in the lower end of said kiln a temperature suflicient to effect the clinkering' of the material at said lowerend, and predetermining or adjusting the {rate of supply of the material and the rapidity of rotation of the kiln with respect to the pitch, diameter, and length of the kiln and to the distribution, quantity and intensity of the heat within the kiln and with respect to the work which must be done on the material to bring it to the clinkering temperature, for the purpose and with the result of. controlling the heaviness of the feed and the extent of exposure of the material to the'heat and thereby controlling the time of the clinkering reaction, substantially as described.

3. In the art of making Portland cement, the process which consists in subjecting lime rock and cement'rock in suitable proportions for a desired period to a temperature surficient to calcine a desired portion of the calcium carbonate content; preparing from said product a finely ground and thoroughly mixed cement form material containing lime and silica in suita le proportions {feeding said material into a rotary kiln; generating in the lower end of said'kiln a temperature sufficient toefi'ect the clinkering of the material at said lower end; and red'etermining or adjusting the rate of fee the heaviness of the feed, and the rapidity of rotation of the kiln with respect to the length-of the kiln and to the distribution, uantity and intensity of the heat within the kiln and with respect to the work which must be done on :the material to bring it to the clinkering' temperature', for the purpose and with the result extent of the clinkering reaction, substantially as described.

4. In the art of making Portland cement, the processwhich consists in burning coal in contact with min led lumps of lime rock and cement rock, fine y grinding and thoroughly mixing the product 'of' said burning operation; feeding said material into a rotary kiln; generating in the lower end of said kiln a temperature sufficient to 'eliect the clinkering of the material at said lower end; and predetermining or adjusting the rate of feed, the heaviness of the feed, and the rapidity of rotation of the kiln with respect tothe length of the kiln, and to the distribution, uantity and intensity ofthe heat within the kiln and with respect to the work which must be done .on the material to bringjt to the clinkering of controlling the time and tempering the 1. In the art of making Portland cement,-

tem erature, for the purpose and with the 'resu t of controlling the time and extent of the clinkeri'ng' reaction, substantially as described.

5. In the art of making Portland cement, the method which consists in burning natural lime rock and-cement rock mixed in proportions so that the average lime, silica, and

alumina contents will be approximately those required for Portland cement clinker, finely grinding the burned product; Feeding said material into a rotary kiln ,generatihg in the lower end of said kiln a temperature 7 sufficient to effect the clinkering of the material at said lower end; and predetermining or adjusting the rate of feed, the heaviness of the feed, and the ra idity of rotation of the kiln with respect tot e length of the kiln and to the distribution, quantity; and intensity of the-heat within the kiln and with respect to the Work which must be done on the materialto bring it to the clinkering temperature, for the'purpose and With the result of controlling the time and tempering the extent of the clinkering reaction, substantially as described.

Signed at New York city, in the county of New} York and State oft New York this 

